1. Field of the Invention
The present invention relates to an electronic device and, more in particular, it relates to an electronic device having a connector for electrical connection with outside typically represented by an engine control unit (also abbreviated as ECU, hereinafter).
2. Description of the Related Art
Usually, electronic devices are subjected to heat cycle test before shipping. In particular, since the temperature in the vehicle changes greatly depending on on-off of an engine or change of circumstantial temperature, an electronic control device mounted on an automobile such as ECU is required to have a specification capable of withstanding to temperature cycles for a wide temperature region (usually, from −40 to 120° C.: based on the General Rules of Environmental Testing Methods for Automotive Electronic Equipment; JASO D001-94, established by Society of Automotive Engineers of Japan, Inc).
For such a temperature range, printed circuit boards having glass epoxy base member (described simply as FR4-type board, hereinafter) have been used generally for electronic circuits board since they are inexpensive.
An epoxy resin as a base member (a material utilized for the base member) of the FR4-type board has a glass transition temperature (also abbreviated as Tg, hereinafter) of about 125° C. which is soft and flexible particularly at high temperature. In ECU using such FR4-type board, the ECU is electrically connected with an external circuit as follows. At first, an opening is formed to an aluminum diecast for securing an electronic circuit board mounted with ECU. The electronic circuit board and the aluminum diecast are secured by fitting a connector main body having pin (for example, plural pins) into the opening of the aluminum die cast (base member formed with the pin). Then, pins for the connector (also referred as connector pins, hereinafter) are inserted into through holes extending through the electronic circuit board (FR4-type board). Then, the through holes and the pin are connected by soldering (such connection form is also referred as through hole connection, hereinafter).
FIG. 9 shows the cross sectional structural view of an existent (conventional) printed circuit board ECU.
A “continuous through hole” described in this specification is characterized, for example, by having an opening formed by being extended between main surfaces on both sides of the electronic circuit board, into which a member being inserted into or penetrating the electronic substrate is fitted. In other words, the continuous through hole, in view of essential feature that it is formed as an opening passing through the electronic board in the direction of the thickness, is distinguished from a so-called “usual through hole” with a main purpose of electrical connection between a plurality of conductive layers formed in the electronic board (isolated from each other in the direction of the thickness of the electronic board) in this specification.
The prior art concerning the connector (connector device) described above includes JP-A No. 6-76887 that discloses a reinforced structure for a pin portion by resin filling in a connector device.